Overview of the Zebrafish System. The zebrafish is now established as a viable complement and alternative to rodents for modeling human development and disease. The Zebrafish core (CORE B) has led the way in generating and collecting a unique repository of zebrafish hematopoietic mutants available for distribution to the international scientific community. The Center had a leadership role in the Trans-NIH Zebrafish Genome Initiative. CORE B has advanced the zebrafish model system by developing new tools and technology, and provided these, and related resources, to researchers who use the fish to study hematopoiesis and other processes.